feat: add Decode Ways

Author: dukeluo

README.md

@@ -81,10 +81,11 @@ Roadmap: https://neetcode.io/roadmap
 | 17   | [Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/)                                         | Medium     | [ts](./TypeScript/17.letter-combinations-of-a-phone-number.ts)                                | Backtracking     |
 | 70   | [Climbing Stairs](https://leetcode.com/problems/climbing-stairs/description/)                                                                                     | Easy       | [ts](./TypeScript/70.climbing-stairs.ts)                                                      | 1-D DP           |
 | 746  | [Min Cost Climbing Stairs](https://leetcode.com/problems/min-cost-climbing-stairs/description/)                                                                   | Easy       | [ts](./TypeScript/70.climbing-stairs.ts)                                                      | 1-D DP           |
-| 198  | [House Robber](https://leetcode.com/problems/house-robber/description/)                                                                                           | Medium     | [ts](./TypeScript/70.climbing-stairs.ts)                                                      | 1-D DP           |
+| 198  | [House Robber](https://leetcode.com/problems/house-robber/description/)                                                                                           | Medium     | [ts](./TypeScript/198.house-robber.ts)                                                        | 1-D DP           |
 | 213  | [House Robber II](https://leetcode.com/problems/house-robber-ii/description/)                                                                                     | Medium     | [ts](./TypeScript/213.house-robber-ii.ts)                                                     | 1-D DP           |
 | 5    | [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/description/)                                                         | Medium     | [ts](./TypeScript/5.longest-palindromic-substring.ts)                                         | 1-D DP           |
 | 647  | [Palindromic Substrings](https://leetcode.com/problems/palindromic-substrings/description/)                                                                       | Medium     | [ts](./TypeScript/647.palindromic-substrings.ts)                                              | 1-D DP           |
+| 91   | [Decode Ways](https://leetcode.com/problems/decode-ways/description/)                                                                                             | Medium     | [ts](./TypeScript/91.decode-ways.ts)                                                          | 1-D DP           |
 
 ### Others
 

TypeScript/91.decode-ways.ts

@@ -0,0 +1,24 @@
+// dp [i] = dp[i+1] + dp[i+2]
+function numDecodings(s: string): number {
+  const dp = { [s.length]: 1 };
+
+  for (let i = s.length - 1; i >= 0; i--) {
+    if (s[i] === "0") {
+      dp[i] = 0;
+    } else {
+      dp[i] = dp[i + 1];
+    }
+
+    if (
+      i + 1 < s.length &&
+      (s[i] === "1" || (s[i] === "2" && "0123456".includes(s[i + 1])))
+    ) {
+      dp[i] = dp[i] + dp[i + 2];
+    }
+  }
+
+  return dp[0];
+}
+
+console.log(numDecodings("226"));
+console.log(numDecodings("106"));